A 30 GHz Real-Time Digitizing OscilloscopeFebruary 12, 2009

Why Would You Need 30 GHz?Bandwidth requirements related to signal speed

Normalized frequency in units of bit rateNormalized frequency in units of bit rate

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55thth harmonic harmonic

This plot shows Power Spectral Density (PSD) as a function of bit rate.

The plot is bounded by rise times that represent 0% (red line) or 100% (blue line) of a Unit Interval (UI)

Typically, serial data rise times are ~30% of a UI. There is significant PSD beyond the 5th harmonic frequency

Using an oscilloscope with bandwidth of 3x the bit rate or higher will show more frequency content

Bandwidth limiting of a 3 Gbps signal demonstrates need for more bandwidth

9 GHz bandwidth limited (3x bit rate)

7.5 GHz bandwidth limited (2.5x bit rate)

Serial data standards ≥2.5 Gb/sMinimum bandwidth requirements

SpecificationBit Rate Bandwidth (2.5x bit

rate)Bandwidth (3x bit

rate)

PCIE 2.0 2.5 Gbps 6.25 GHz 7.5

DisplayPort 1.1 2.7 Gbps 6.75 GHz 8.1 GHz

SATA 3 Gbps 7.5 GHz 9 GHz

SAS 3 Gbps 7.5 GHz 9 GHz

HDMI 1.3 a/b/c 3.4 Gbps 8.5 GHz 10.2 GHz

SuperSpeed USB 4.8 Gbps 5.76 GHz 14.4 GHz

SAS 6 Gbps 15 GHz 18 GHz

SATA 6 Gbps 15 GHz 18 GHz

Fibrechannel 8.5G 8.25 Gbps 20.625 GHz 24.75 GHz

PCIE 3.0 8 Gbps 20 GHz 24

10GBASEKR(802.3ap-2007

Backplane Ethernet)

10.3125 Gbps 25.78125 GHz 30.9735

Serial data transfer rate increases drive“Moore’s Law of Oscilloscope Bandwidth”

2000 Gigabit ethernet 1.25 Gbps

2001 SAS I 1.5 Gbps

2002 SATA I 1.5 Gbps

2003 PCI Express I 2.5 Gbps

2004 SAS I 3 Gbps

2005 XAUI 3.125 Gbps

2006 PCI Express II 5 Gbps

2007 SAS II 6 Gbps

2008 PCI Express III 8 Gbps

2009 10GBase-KR 10.3125 Gbps Dat

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As serial data transfer rates increase, the unit interval decreases and the rise time decreases, driving the need for more oscilloscope bandwidth

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2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012

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z)“Moore’s Law of Oscilloscope Bandwidth”Driven by Increasing data transfer rates and decreasing rise times

1st generation (6-8 GHz)

2nd generation (13 - 16 GHz)

“Moore’s law for bandwidth

Oscilloscope bandwidth

Problem – Serial data transfer rates and rise times of serial data signals require doubling of oscilloscope bandwidth every three years

Reality – Oscilloscopes must stay ahead of this curve while using the devices driving the curve

Methods for increasing oscilloscope bandwidth

DSP bandwidth boosting (stretching) Apply a digital filter to the acquired waveform that has a response which

peaks near the cutoff frequency of the input amplifier Peak in the filter response pushes the 3dB point up in frequency Can increase high frequency noise Sampling rate must be > 2X the boosted frequency Limited boost range based on the transition band of the input amplifier

Bandwidth interleaving Utilize RF hardware to digitize the signal in different frequency bands Use DSP filters to combine the separately digitized bands into one

waveform sampled at 2x the rate Front end amplifiers are always operating comfortably in rated frequency

range Reduces channel count but doubles the bandwidth No additional increase in high frequency noise Uses standard RF components (mixers, filters, amplifiers)

DSP bandwidth boostingNot the preferred method for increasing bandwidth

Amplifier responseDSP filter response

Boosted response

f fboosted

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Note: DSP “boost” or “stretch” should not be confused with other uses of DSP in oscilloscopes, such as to make minor response changes to match the response of channels and gain ranges or adjust phase delay. In the latter cases, DSP will provide signal fidelity improvements, not reductions.

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DSP bandwidth boosting is not a viable solution for meeting market demands

1st generation (6-8 GHz)

2nd generation (13 - 16 GHz)

“Moore’s law for bandwidth

Oscilloscope bandwidth

Tektronix attempted to keep up with “Moore’s Law of Oscilloscope Bandwidth” using a DSP boost (see yellow dotted line)

Unfortunately, the impact was limited, and oscilloscope bandwidth was again insufficient to meet market demand

Digitizer InterleavingAn accepted method to increase SR and memory

Bandwidth set by front-end amplifier

Lower speed digitizers and memory interleaved Improves sampling rate of A/D

Multiplies A/D converter sampling rate

Front-end amplifier

ADC’s

memory

Bandwidth InterleavingAn innovative method to stay ahead of the BW curve

Separate signal into frequency bands

Down-convert high band to low frequency

Digitize down-converted and low-band simultaneously

Use DSP to compensate delay, phase and amplitude and combine bands

40 G sa/s ADC’s

memory

16 – 30 GHz

1 – 15 GHz

0 – 16 GHz

DSP channel combiner

31.25 GHz LO

30 GHz @ 80 G sa/s

Bandwidth Interleaving – Animation

DBI Animation - Click Here

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2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012

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z)DBI allows oscilloscopes to keep up with “Moore’s Law of Oscilloscope Bandwidth”

1st generation (6-8 GHz)

2nd generation (15 - 16 GHz)

DBI

LeCroy’s DBI enables oscilloscopes to remain ahead of the bandwidth curve using current generation chip technology (solid yellow line)

LeCroy oscilloscope design allows for easy upgrade from 4 to 30 GHz bandwidth

WaveMaster 4 to 16 GHz acquisition board hardware

WaveMaster 20 to 30 GHz acquisition board hardware just adds DBI modules and 2.92mm

front panel connectors

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LeCroy WaveExpert sampling oscilloscope Measurement of “golden” step response

Input Step measured with WaveExpert Sampling Scope with 70 GHz sampler Usually subtract the input risetime from the measured risetime to get the

“scope only” risetime 22 Risetime InputRisetime MeasuredRisetimeOnly Scope

Step response measured on 30 GHz WaveMaster 830 Zi (DBI) oscilloscope

Shape of step and rise time value closely correlate with sampling scope

Step response measured on 30 GHz WaveMaster 830 Zi (DBI) oscilloscope

Oscilloscope bandwidth (top plot) shows response out to 30 GHz.

Conclusion

Bandwidth requirements are being driven by increasing transfer rates (and decreasing rise times) Oscilloscope hardware performance (amplifiers and A/D converters) is

set by the current technology Next generation hardware must be measured by current generation

technology

Oscilloscope bandwidth is being driven by a “moore’s law” which requires a doubling every 3 years

Bandwidth stretching using DSP cannot keep up with the bandwidth need and has limited performance

LeCroy’s Digital Bandwidth Interleaving (DBI) enables the doubling of current technology enabling measurements on next generation hardware

LeCroy’s DBI is the best way to achieve high bandwidth with appropriate signal fidelity